Historically, re-refining waste oil has been difficult to undertake economically unless conducted on a large scale. While complex large scale processing facilities for recycling waste oils and converting them to reusable products are known, due to the expense of the known technologies, these large-scale capital intensive process facilities are required to draw on large geographical catchment areas for waste oil feedstock. Due to feedstock, transportation, and logistics costs, which may quickly consume any economies of scale benefit, large scale processing facilities are only viable in large regional markets able to supply sufficient quantities of waste oil feedstock within a reasonable distance. In smaller and developing markets where such large scale operations are not sustainable, it has not been possible to economically re-refine waste oils with known technology.
Current practices in markets too small to support conventional re-refining facilities include burning waste oil as a dirty fuel for industrial use or space heating, or alternatively disposing of large volumes of waste oil in potentially environmentally inappropriate ways. These practices may result in a discharge of air borne pollutants, or contamination of soils and groundwater. Whichever practice is used, the resulting water, soil, and/or air pollution contains many of the harmful chemicals found in waste oil, which may expose plants, animals and humans to their toxic effects. Therefore, in many jurisdictions around the world waste oil is mostly classified as a hazardous waste material.
What is needed is a solution to recycle these waste oils in a more environmentally friendly and economically viable manner. The ideal solution is an economically viable micro scale waste oil re-refining or conversion process operable with feedstock obtained from a smaller population area. Of course, an essential and key component of such a re-refining/conversion process is a cracking vessel or reactor where waste oil is thermally cracked and decomposed into diesel fuel range hydrocarbons. The existing technologies and processes available for decomposing waste oil includes re-refining process and reactors of various capacities, shapes, designs and with differing operating methods. However, the existing technologies have failed to address the needs for re-refining in small population centres. They have failed to create a continuous and economically viable process. These re-refineries have also failed to address low yield and the formation of coke sludge in the processes.
The present method and device is built to overcome precisely these obstacles, conducting pyrolysis of waste oil and converting to diesel fuel range hydrocarbons in a miniaturized scale that is commercially viable. The invention allows for the continuous pyrolysis of smaller amounts of feedstock to be converted into valuable petroleum distillates. This method and device reduces the cost of waste oil re-refining. It achieves this through an optimum residence time under sub atmospheric pressures during the pyrolysis reaction. The process does not use any catalyst and has almost no coke formation inside the reactor or in any other part of the process relative to other prior art. The invention is designed to maximize the process yield of diesel fuel by-products without subjecting the method or the reactor to undesired conditions. Consequently, the reactor does not require a high frequency of cleaning nor does it require the installation of a bleeding pump or a scrapper-like apparatus to continually address the formation of coke inside of the reactor. The device also operates on a continuous basis, thereby causing minimal disruption to overall operations and reducing the need to have either multiple reactors or operating in batches or semi-continuous flow.
There are a number of existing methods/processes for converting waste oils to diesel or diesel-like fuels. For example, U.S. Pat. Nos. 5,271,808 and 5,286,349 issued to Shurtleff disclose a process and equipment design for converting waste oil to diesel. However, although designed with a direct fired heat, the design of the pan shaped reactor and the rest of the systems are dramatically different from the present invention. The process uses a desludging pre-processor to remove the sludge/coke pre-cursor materials from the feedstock. The baffle arrangement within the reactor is intended to direct any heavy materials in the reactor to a draw off point. However, this design element ensures that the sludge/coke forming material spends a lot of time near the hottest part of the reactor resulting in increased coke formation. As a result significant operating and maintenance costs are incurred and loss of production is suffered for the removal and disposal of coke and other heavy by-products.
A number of approaches have been developed to attempt to overcome the coke formation issue and the resultant difficult to control operation. For example, U.S. Pat. No. 5,885,444 issued to Wansbrough et al. discloses a system where the heat for pyrolysis of the waste oil is provided by high volume circulation of the waste oil through an external heat recovery system and reactor system. In addition, a heavy fuel oil containing coke particles and potential coke precursors is continuously removed from the reactor vessel. The heavy fuel oil stream is withdrawn at a rate of approximately 25% of the inlet feed rate and thus significantly reduces the overall process yield to diesel fuel.
As another example, U.S. Pat. No. 6,132,596 issued to Yu discloses a system where the design of the process and reactor is the most different from the present invention. The method employed uses a design where pyrolysis heat is added via rapid circulation of waste oil from a reactor vessel, through the tubes of a fired heater and back into the reactor vessel under high pressure. As the reaction proceeds, coke and coke precursors build up in the reactor and on the walls of the fired heater tubes, requiring the operator to subject the process to a high temperature treatment to convert all residual material to coke. The coke then must be physically cleaned from the inside of the reactor and the fired heater tubes.
Another example, U.S. Pat. No. 5,871,618 issued to Lee et al. discloses a semi-continuous thermal cracking process. The design of the thermal cracking reactor is U-shaped or bathtub shaped. In another model, the bottom is circular. The reactor is located within a combustion chamber comprising multiple burners placed below and along the side of the reactor vessel. The combustion chamber is designed so that the top can be removed and the bottom or the reactor accessed and/or removed for maintenance or cleaning. Heavy materials that do not crack in the initial portion of the process are treated in a batch manner where it is heated to a much higher temperature and turned into a coke containing excess carbon, solid residues and heavy metals. The process requires pausing inflow of feedstock every 50 hours of operation. The reactor heating continues until the remaining waste oil is completely used up inside the reactor, followed by at least 26 hours to coke residual material to ash cake, to allow ash cake to cool down and finally to remove ash cake from the reactor. After cooling, the reactor must be opened and additional time is needed to physically clean the reactor and then bring it back on line and heat it up to operating temperature again.
An improvement on the process and/or device is claimed in U.S. Pat. No. 7,255,785 issued to Kong and Jeong but it is still a semi-continuous process, results in solidifying sludge cake which must then be removed by means of a bleeding valve at the bottom of the vessel and the process results in only 70 percent conversion of feedstock. The process uses Argon gas at the beginning of the process to pre-pressurize the reactor to a pressure substantially above the atmospheric pressure. It is not abundantly clear if the heat is provided by a fired heater.
Finally, WIPO Patent Application No. 2005/087897 to Baker also refers to a process for conversion of waste plastic and waste oil to liquid fuel but again this process is semi-continuous, uses a catalytic converter after the pyrolysis reactor to affect the desired degree of conversion, operates above atmospheric pressure and uses an scrapping device located inside the reactor to address the formation of solid by-products on the walls of the reactor.